Google's YouTube is dropping future feature upgrade support for certain older browsers, most notably Internet Explorer 6 for Windows. But reader Mike Lemon discovered and alerted us that the last release of Firefox for Mac OS X 10.3.9 Panther - version 18.104.22.168 - will also be dropped from supported browsers. Safari 1.3.2, the, is also too old for further development.
YouTube that dropping support doesn't mean videos will no longer play in older browsers. Rather, new features won't be engineered to work on these ancient releases. YouTube will fully support Firefox 3.0+, Chrome 4.0+, Internet Explorer 7.0+, Opera (no version noted), and Safari 3.0+.
Panther users who want to have access to future YouTube improvements have just one choice that I can find: Opera 10, which is with both Intel- and PowerPC-based Macs.
While Panther users may be stuck in time, Mac OS X 10.4 Tiger users have access to the latest version of Firefox (3.6) and, among other browsers. (The Mozilla Foundation that manages the code base used for Firefox, Camino, and other browsers said on 8 February 2010 that it would  in the rendering engine that will be part of Firefox 3.7.)
YouTube started inserting interstitial messages in mid-2009 to warn users of older browsers; the message requires a click to bypass and view a video. The messages were set to appear every two weeks - ostensibly relying on cookies to avoid repeating. This is the first I've heard of it, and there's scant documentation on the Internet about it.
 that, as of 1 March 2010, Google Apps will stop supporting older browsers too. Google will start by phasing out support in Google Docs and Google Sites, and the elimination of support will no doubt make its way out to other Google services over time as well.
Frankly, we're entirely in favor of Google taking a stand on the use of these old browsers, Internet Explorer 6 in particular. The TidBITS Web site has never rendered well in Internet Explorer 6 because its support for basic Web standards was so lacking, and we couldn't justify spending significant time and effort on such an old browser for a non-Apple platform. It's a little too bad that those people left on Mac OS X 10.3 Panther will start to see a loss of functionality, but those older browsers simply don't have the capabilities Web developers need to offer a modern Web site.